Do peptide mimetics of gp41 improve antibody-epitope interactions? Abstract In this F32 application I postulate that the broadly HIV neutralizing monoclonal antibodies, 2F5 and 4E10, against the membrane proximal external region (MPR) of gp41 were induced in a small population of donors by MPR epitopes due to modifications in the envelope proteins. My idea is to generate MPR immunogens incorporating unnatural amino acids that may induce stronger immune responses. I believe that these novel peptides will induce stronger affinity toward monoclonal antibodies, 2F5 and 4E10, and potentially induce higher titer polyclonal antibodies in a prime-boost immunization assay. The idea to use unnatural amino acids is unique. MPR immunogen design has focused on eliciting antibody responses that cross-react with phospholipids because the mAbs 2F5 and 4E10 exhibit unusual cross-reactivity with phospholipids. Incorporation of chemically modified amino acids into known epitopes may induce stronger immune responses. I will synthesize a group of MPR-based peptide sequences containing modified residues, which will be used to determine antibody affinity using a BIAcore assay. Structure activity relationships will be derived from these data and will guide subsequent rounds of chemically modified peptides to find sequences that will bind optimally to the monoclonal antibodies. I will then determine the immunogenicity of each peptide in rabbits using a prime-boost immunization strategy. Lipopeptides based on the peptides used in the BIAcore assay will be presented in a liposomal formulation to further enhance immunogenicity by presenting the epitopes in a lipid bilayer. Rabbits will be immunized subcutaneously and intramuscularly and antisera from these animals will be obtained and evaluated in a validated ELISA assay to determine the antibody titer induced by each peptide immunogen. Furthermore, formulations containing the same lipopeptides will be delivered intranasally to evaluate the mucosal immune response. Formulations will be prepared in the presence and absence of a peptide that binds and is transported by the neonatal Fc receptor (FcRn). ELISA assays will be used to determine the antibody responses in serum from SC/IM immunized animals, while mucosal lavage and serum samples will be evaluated from IN immunized animals. Differences in antisera titers from SC/IM immunized animals will be compared to IN immunized animals. Antisera and mucosal lavage samples with high titers in rabbits will be used in traditional inhibition assays to determine the neutralization activity of primary HIV-1 isolates in PBMCs. Success in generating neutralizing antibodies in rabbits will lead to future work to generate monoclonal antibodies. The chemically modified peptides that induce neutralizing antibodies in rabbits could provide a widely applicable epitope design strategy for the development of vaccines to a variety of infectious diseases including HIV.